Production of field-reversed plasma with a magnetized coaxial plasma gun

Abstract

Experimental data are presented on the production of field-reversed deuterium plasma by a modified coaxial plasma gun. The coaxial gun is constructed with solenoid coils along the inner and outer electrodes that, together with an external guide field solenoid, form a magnetic cusp at the gun muzzle. The net flux inside the inner electrode is arranged to be opposite the external guide field and is the source offield-reversed flux trapped by the plasma. The electrode length is 145 cm, the diameter of the inner (outer) electrode is 15 cm (32 cm). The gun discharge is driven with a 232-/lF 40-k V capacitor bank. Acceleration of plasma through the magnetic cusp at the gun muzzle results in entrainment offield-reversed flux that is detected by magnetic probes 75 cm from the gun muzzle. Field-reversed plasma has been produced for a variety of experimental conditions. In one typical case, the guide magnetic field was Bo = 4.8 kG and the change in axial magnetic field .::iB, normalized to Bo was .::iB,/Bo = -3.1. Total field-reversed flux (poloidal flux) obtained by integrating .::iB, profiles is in the range 2 X 10 3 kG cm 2 • Measurement of the orthogonal field component indicates a sizable toroidal field peaked off axis at r~ 10 cm with a magnitude of roughly one-half the poloidal field component that is measured on magnetic axis. Reconnection of the poloidal field lines has not been established for the data reported in the paper and will be addressed in future experiments which attempt to trap and confine the field-reversed plasma in a magnetic mirror.

Scaling studies of spheromak formation and equilibrium

“…Spheromak formation by magnetized coaxial plasma gun has been discussed both theoretically and experimentally. [14][15][16][17] The fundamental idea in all this work is that a threshold value of th ϭ 0 I gun /⌽ gun must be exceeded in order that a spheromak is formed. The dimensions of th are an inverse length so one expects the threshold parameter to be some constant of order unity divided by the scale of the system.…”

Generalization of cylindrical spheromak solution to finite beta and large reversed shear

“…A commonly used force-free spheromak equilibrium is the so-called Bessel-function model ͑also called the Chandrasekhar-Kendall model͒ which is based on the assumptions that the configuration is symmetric about the z axis and is enclosed by a perfectly conducting cylindrical shell having radius a and height h. 5,8,9 The purpose of this paper is to generalize the ␤ϭ0 Bessel function solution to finite ␤ situations and to make a preliminary consideration of the ramifications of finite ␤. We note that finite ␤ spheromak equilibria have been calculated previously, 10-13 but these equilibria were not generalizations of the cylindrical Bessel function solution.…”

Improvement of Sensor for Noncontact Capacitance/Voltage Measurement and Lifetime Measurement of Bare Silicon(100)

“…The technical operation of CTX is similar to that of the Beta-II experiment at Livermore National Laboratory [14,1] and the CTCC-I experiment at Osaka University [15]. Primary differences include 1. long-pulse sustainment by helicity injection [9]; 2. use of mesh flux conserver [13]; 3. operation with filling gas to replace particle loss [2].…”

“…In addition to this power loss, there should also be an additional loss from the P dV work done in replacing the particles [25], as pointed out for spheromak transport by Meyerhofer [5]. Thus the volume average, particle replacement, power density loss in the electron temperature balance equation would be a v^l^+ 30 eV/ionization 1 (14) where T P is the global particle confinement time.…”